Bumper collision sensor

ABSTRACT

A bumper collision sensor can detect collision without hurting a pedestrian even if a bumper is deformed significantly. The bumper collision sensor includes a wire, a tension sensor, and a substrate. The wire has an extendable portion in a part thereof. The tension sensor is connected to one end of the wire. The substrate is mounted with the tension sensor and the wire and is attached, with plasticity, to the bumper. The tension sensor is fixed to one end of the substrate. The wire is arranged in the tension sensor along a longitudinal direction of the substrate with a stress equal to or lower than a value set in advance. The other end of the wire is fixed to the substrate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a bumper collision sensor foran automobile and the like for detecting collision with a pedestrian.

2. Description of the Related Art

In recent years, from the viewpoint of protection of pedestrians intraffic accidents, there has been a worldwide tendency toward theestablishment of pedestrian protection rules for automobiles. The rulesaim at reducing a degree of injuries suffered by a pedestrian when anautomobile collides with the pedestrian. Various pedestrian protectionsystems have been conventionally proposed. For example, there are asystem for, when collision with a pedestrian is detected, lifting a hoodto prevent a head of the pedestrian from colliding with a hard engineunit and a system for, when collision with a pedestrian is detected,expanding an airbag over a hood. These systems attract attention assystems for actively reducing head injuries of pedestrians and aredeveloped extensively.

These pedestrian protection systems require a bumper collision sensorfor detecting collision with a pedestrian. As such a bumper collisionsensor, a bumper collision sensor using a load sensor is proposed. Aplan view of the load sensor is shown in FIG. 14 and an output waveformchart of the load sensor is shown in FIG. 15.

In FIG. 14, load sensor 1 includes sensor cells 1 b that are formed onbelt-like sensor film 1 a by screen printing or the like. When a load isapplied to sensor cells 1 b, a voltage, which is an output of sensorcells 1 b, changes in proportion to a magnitude of the load. Pluralsensor cells 1 b are formed substantially at equal intervals in alongitudinal direction of sensor film 1 a. Load sensor 1 with such aconstitution is arranged in a longitudinal direction of a bumper of anautomobile.

When the automobile collides with a pedestrian, a load corresponding toimpact caused by the collision is applied to load sensor 1 arranged inthe bumper. As shown in FIG. 15, a sensor output rapidly increases whenthe automobile collides with the pedestrian but then rapidly decreaseswhen the pedestrian is sent flying. Therefore, a waveform of the sensoroutput has a peak when the automobile collides with the pedestrian. Inthis case, the peak is large when the automobile collides with an adultand is small when the automobile collides with a child.

On the other hand, when the automobile collides with a fixed object suchas a wall or a pillar, a sensor output rapidly increases and then a loadcontinues to be applied to the sensor cells 1 b because the fixed objectis never sent flying. As a result, as a waveform of the sensor output,the sensor output continues to increase gently without decreasing.

Consequently, load sensor 1, which is the conventional bumper collisionsensor, can not only detect collision but also judge whether a collisionobject is a human or an object according to whether a peak value in timewidth T in FIG. 15 is in an output range for a human (between S1 to S2).

The conventional constitution is disclosed in JP-A-2004-276885.

However, although it is certainly possible to detect collisiondistinguishing a human and an object by using load sensor 1 in thebumper collision sensor, it is necessary to accurately obtain a waveformshown in FIG. 15 for the detection. Therefore, load sensor 1 has to befirmly fixed to the bumper.

On the other hand, from the viewpoint of pedestrian protection, in orderto reduce damage to the legs of a colliding pedestrian to which damageare applied first, a shock absorbing structure, which is adapted to beeasily deformed, tends to be adopted for a bumper. It is known that anamount of deformation of the bumper at the time when a pedestriancollides with the bumper is about a diameter of a femoral region of oneleg. This is equivalent to about 15 to 20 cm in a standard physique.

Since load sensor 1 firmly fixed to the bumper is a belt-like sensorconsisting of sensor films 1 a, when load sensor 1 is subjected to suchdeformation due to collision, it is likely that load sensor 1 is brokenduring the deformation of the bumper if load sensor 1 is stretched onthe order of several tens of centimeters. As a result, it is likely thata sensor output is interrupted during measurement of the waveform shownin FIG. 15 to make it impossible to detect collision.

To cope with the problem, it is conceivable to make sensor films 1 astrong such that sensor films 1 a are not broken. In this case, loadsensor 1 is not deformed even if the bumper is deformed at the time ofcollision of a pedestrian. Thus, it is likely that load sensor 1 willhurt the legs of the pedestrian. When sensor film 1 a is made of a softmaterial such as rubber, sensor cells 1 b move according to deformationof the bumper. This could make it hard to measure an accurate load.

SUMMARY OF THE INVENTION

The invention provides a bumper collision sensor that can detectcollision without hurting a pedestrian even if a bumper and a substrateare deformed significantly.

The bumper collision sensor of the invention includes a wire having anextendable portion in a part thereof, a tension sensor connected to oneend of the wire, and a substrate that is mounted with the tension sensorand the wire and attached, with plasticity, to a bumper. The tensionsensor is fixed to one end of the substrate. The wire is arranged in thetension sensor along a longitudinal direction of the substrate with astress equal to or lower than a value set in advance. The other end ofthe wire is fixed to the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a schematic perspective view of a bumper collision sensor in afirst embodiment of the invention;

FIG. 2A is a diagram of a state in which a wire is fit in betweenprojections of the bumper collision sensor in the first embodiment;

FIG. 2B is a diagram of a state in which a wire holding member is fitinbetween the projections of the bumper collision sensor in the firstembodiment;

FIG. 2C is a diagram of a state in which heat press is applied to theprojections of the bumper collision sensor in the first embodiment;

FIG. 2D is a diagram of a state in which integration of the wire holdingmember in the projections of the bumper collision sensor in the firstembodiment is completed;

FIG. 3 is a partial sectional view showing a structure of a tensionsensor in the bumper collision sensor in the first embodiment;

FIG. 4 is a schematic sectional view of a tension detecting unit in thebumper collision sensor in the first embodiment;

FIG. 5 is a waveform chart showing a changing component after excludinga DC component from an output of the bumper collision sensor in thefirst embodiment;

FIG. 6 is a flowchart describing operations of the bumper collisionsensor in the first embodiment;

FIG. 7 is a schematic perspective view of a bumper collision sensor in asecond embodiment of the invention;

FIG. 8A is a diagram of a state in which a wire is fit in betweenprojections of the bumper collision sensor in the second embodiment;

FIG. 8B is a diagram of a state in which a wire holding member is fitinbetween the projections of the bumper collision sensor in the secondembodiment;

FIG. 8C is a diagram of a state in which heat press is applied to theprojections of the bumper collision sensor in the second embodiment;

FIG. 8D is a diagram of a state in which integration of the wire holdingmember in the projections of the bumper collision sensor in the secondembodiment is completed;

FIG. 9 is a partial sectional view showing a structure of a tensionsensor in the bumper collision sensor in the second embodiment;

FIG. 10A is a diagram of a wire in a normal (non-collision) state in aschematic diagram showing a wire deformation pattern according to acollision position in the bumper collision sensor in the secondembodiment;

FIG. 10B is a diagram of a wire state upon a left collision in theschematic diagram of the bumper collision sensor in the secondembodiment;

FIG. 10C is a diagram of a wire state upon a center collision in theschematic diagram of the bumper collision sensor in the secondembodiment;

FIG. 10D is a diagram of a wire state upon a right collision in theschematic diagram of the bumper collision sensor in the secondembodiment;

FIG. 10E is a diagram of a wire state upon left and center collisions inthe schematic diagram of the bumper collision sensor in the secondembodiment;

FIG. 10F is a diagram of a wire state upon left and right collisions inthe schematic diagram of the bumper collision sensor in the secondembodiment;

FIG. 10G is a diagram of a wire state upon center and right collisionsin the schematic diagram of the bumper collision sensor in the secondembodiment;

FIG. 10H is a diagram of a wire state upon left, center, and rightcollisions in the schematic diagram of the bumper collision sensor inthe second embodiment;

FIG. 11 is a flowchart describing operations of the bumper collisionsensor in the second embodiment;

FIG. 12 is a schematic perspective view of a bumper collision sensor ina third embodiment of the invention;

FIG. 13A is a diagram of a normal wire state in a schematic diagramshowing a wire deformation pattern according to a collision position inthe bumper collision sensor in the third embodiment;

FIG. 13B is a diagram of a wire state upon a left collision in theschematic diagram of the bumper collision sensor in the thirdembodiment;

FIG. 13C is a diagram of a wire state upon a center collision in theschematic diagram of the bumper collision sensor in the thirdembodiment;

FIG. 13D is a diagram of a wire state upon a right collision in theschematic diagram of the bumper collision sensor in the thirdembodiment;

FIG. 13E is a diagram of a wire state upon left and center collisions inthe schematic diagram of the bumper collision sensor in the thirdembodiment;

FIG. 13F is a diagram of a wire state upon left and right collisions inthe schematic diagram of the bumper collision sensor in the thirdembodiment;

FIG. 13G is a diagram of a wire state upon center and right collisionsin the schematic diagram of the bumper collision sensor in the thirdembodiment;

FIG. 13H is a diagram of a wire state upon left, center, and rightcollisions in the schematic diagram of the bumper collision sensor inthe third embodiment;

FIG. 14 is a plan view of a load sensor that is a conventional bumpercollision sensor; and

FIG. 15 is an output waveform chart of the load sensor that is theconventional bumper collision sensor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the invention will be hereinafter explained withreference to the accompanying drawings.

First Embodiment

FIG. 1 is a schematic perspective view of a bumper collision sensor in afirst embodiment of the invention. FIG. 2A is a diagram of a state inwhich a wire is fit in between projections of the bumper collisionsensor in this embodiment. FIG. 2B is a diagram of a state in which awire holding member is fit in between the projections of the bumpercollision sensor in this embodiment. FIG. 2C is a diagram of a state inwhich a heat press is applied to the projections of the bumper collisionsensor in this embodiment. FIG. 2D is a diagram of a state in whichintegration of the wire holding member in the projections of the bumpercollision sensor in this embodiment is completed.

FIG. 3 is a partial sectional view showing a structure of a tensionsensor in the bumper collision sensor in this embodiment. FIG. 4 is aschematic sectional view of a tension detecting unit in the bumpercollision sensor in this embodiment. FIG. 5 is a waveform chart showinga changing component after excluding a DC component from an output ofthe bumper collision sensor in this embodiment. FIG. 6 is a flowchartshowing operations of the bumper collision sensor in this embodiment.

In FIG. 1, in order to reduce damage to a pedestrian, substrate 11 ismolded out of a material having plasticity and integrally attached tobumper 30 also molded out of a material having plasticity with anadhesive or the like. Plural projections 12 formed in a conical shapewith a circular section are provided to substrate 11 by integral moldingwith substrate 11. It is possible to reduce the number of components byintegrally molding projections 12 and substrate 11. Thus, it is possibleto reduce the likelihood of injuries due to dropping of a componentcaused by collision with a pedestrian.

Wire 13 consisting of a tension spring of stainless steel is set betweentwo projections 12. The tension spring is equivalent to an extendableportion. In the first embodiment, entire wire 13 is constituted as atension spring having an extendable part. An interval of projections 12is set larger than a diameter of wire 13 such that wire 13 is not caughtby projections 12. Note that, although a rubber material havingelasticity may be adopted as the extendable portion, deterioration undera severe environment of an automobile is a concern. Thus, reliability isimproved by adopting a tension spring made of a metal material, inparticular, a stainless steel material having excellent durability.

One end of wire 13 is connected to tension detecting unit 17 (shown inFIG. 3) built in tension sensor 14. Tension sensor 14 is fixed to oneend of substrate 11. Since this part is on a side not colliding with apedestrian, the likelihood of breakage of the sensor due to collision isextremely low. The other end of wire 13 is fixed to projections 12located in a lower left part of FIG. 1 with a part of the tension springconstituting wire 13 fit in projections 12. It is possible to reduce thenumber of components because a new fixing member is unnecessary byfixing wire 13 in this way. It is also possible to reduce the likelihoodof injuries due to dropping of a component caused by collision with apedestrian.

The length of wire 13 is set to a length connecting fixing projections12 and tension sensor 14 such that almost no stress is applied totension sensor 14 when tension sensor 14 is attached as shown in FIG. 1and the stress is equal to or less than a value set in advance.Consequently, since almost no tension is applied to wire 13, vibrationof wire 13 at the time of driving of an automobile is not transmitted totension sensor 14, leading to improvement of reliability.

An intermediate part of wire 13 is integrated in substrate 11 by fittingwire holding members 15 of a columnar shape having a circular section toprojections 12 such that wire 13 does not come off substrate 11. Notethat it is likely that, if projections 12 and wire holding members 15have shapes with corners, wire 13 will be caught by the corners becauseof deformation of substrate 11 caused by collision, and tension of wire13 will not be transmitted to tension sensor 14 accurately. Therefore,projections 12 and wire holding members 15 have circular sections inorder to reduce the likelihood of such occurrences. Moreover, sincethere are no corners, it is also possible to reduce the likelihood thatprojections 12 and wire holding members 15 will hit a pedestrian becauseof deformation of bumper 30 and substrate 11 to hurt the pedestrian.

A method of integrating wire holding member 15 in projections 12 isshown in FIGS. 2A to 2D. Note that FIGS. 2A to 2D show a section takenat a broken line part in FIG. 1. As shown in FIG. 2A, first, wire 13 isinserted between projections 12. As shown in FIG. 2B, projections 12 areinserted into holes (not shown) of wire holding member 15. As shown inFIG. 2C, heat press 16 is pressed against portions of projections 12sticking out from wire holding member 15. Consequently, the sticking-outportions are softened and heated and compressed. Finally, as shown inFIG. 2D, heat press 16 is removed to harden the crushed sticking-outportions and fix wire holding member 15 to projections 12. By adoptingsuch a method, it is possible to integrate wire 13 in substrate 11extremely easily.

Details of tension sensor 14 will be explained with reference to FIGS. 3and 4. FIG. 4 shows a section of a tension detecting portion of tensiondetecting unit 17, that is, a section along line 4-4 in FIG. 3. Notethat, to facilitate understanding, thickness of a structure formed onstainless steel substrate 20 is exaggerated. Tension detecting unit 17is fixed to body 19 by screws 18 in tension sensor 14. Tension detectingunit 17 includes stainless steel substrate 20, electrodes 21, strainresistance element 22, detection circuit 23, insulating layer 24 (notshown in FIG. 3), and protective layer 25 (not shown in FIG. 3).

Stainless steel substrate 20 has a cantilever shape as shown in FIG. 3.Insulating paste containing a glass component is formed on stainlesssteel substrate 20 as insulating layer 24 by printing and sintering. Toensure insulating properties, printing and sintering are performedplural times. Electrodes 21 are formed on the insulating layer 24 byprinting and sintering a conductive paste consisting of particulates ofa metal component. A silver-palladium metal component is used. A wiringpattern (not shown) of detection circuit 23 is also formedsimultaneously.

Strain resistance element 22, a resistance of which changes because ofdistortion, is formed to overlap parts of electrodes 21 on insulatinglayer 24 in a part of a surface of a beam of stainless steel substrate20. Strain resistance element 22 is formed by printing and sintering athick-film resistor paste containing ruthenium oxide conductiveparticles and a glass component. Protective layer 25 is formed to coverstrain resistance element 22 on the surface of strain resistance element22. Protective layer 25 is formed by printing and sintering aninsulating paste containing a glass component having a sinteringtemperature lower than that of insulating layer 24. The tensiondetecting portion of tension detecting unit 17 is constituted in thisway. Since all the components are sintered at temperatures far higherthan environmental temperatures in use, it is possible to secureextremely high reliability.

Detection circuit 23 is formed in a root portion of the beam ofstainless steel substrate 20. Detection circuit 23 is assembled by,after forming protective layer 25, mounting a circuit component (notshown) constituting detection circuit 23 and passing protective layer 25mounted with the circuit component through a soldering reflow oven. Aprotective film of resin for protecting the circuit component is appliedto the entire surface of detection circuit 23.

By adopting the structure described above, it is possible to constitutetension detecting unit 17 integrated with detection circuit 23 extremelyeasily. Consequently, in addition to reduction of cost through reductionof the number of components, it is possible to reduce the likelihood ofinjuries due to dropping of a component caused by collision with apedestrian. Wire 13 is welded and connected to the vicinity of a distalend of the beam. Since both the beam and wire 13 are made of stainlesssteel, it is possible to weld the beam and wire 13. Thus, in addition tosecuring durability of the material itself, it is possible to surelyconnect the beam and wire 13.

Operations in this embodiment will be explained. In general, when anautomobile collides with a pedestrian, no significant injuries arecaused when vehicle speed is less than 20 km per hour. The pedestrian issent flying backward by a hood when vehicle speed exceeds 60 km perhour. Thus, in both the cases, it is difficult to expect an effect evenif a pedestrian safety system is driven. Therefore, as a result ofreading a vehicle speed signal from a vehicle speed sensor mounted onthe automobile, if vehicle speed is 20 to 60 km per hour, the bumpercollision sensor of the invention performs operations described below.

When a pedestrian collides with bumper 30, bumper 30 made of aplasticmaterial and substrate 11 integrally fixed to bumper 30 with an adhesiveor the like are deformed by about several tens of centimeters. As aresult, wire 13 built in substrate 11 is pulled according to thedeformation. In this case, since entire wire 13 is made of a tensionspring, wire 13 extends without being broken and tension of wire 13 istransmitted to tension detecting unit 17 of tension sensor 14.

Stress is applied to tension detecting unit 17 in a direction in whichthe beam provided in a part of stainless steel substrate 20 is pulled.As a result, strain resistance element 22 provided on the surface of thebeam warps and a resistance thereof changes. This change is electricallydetected by detection circuit 23. Detection circuit 23 detects thechange in the resistance of strain resistance element 22 as a change ina voltage. In this case, various DC resistance fluctuation factors suchas aged deterioration and temperature change of strain resistanceelement 22 are cut by a filter circuit (not shown) for cutting a DCcomponent of a voltage. Consequently, reliability of an output isimproved. With the constitution described above, an absolute value oftension is not detected and only an amount of change in tension isoutputted.

An example of an output waveform of tension sensor 14 is shown in FIG.5. In FIG. 5, an abscissa indicates time and an ordinate indicates anoutput. A solid line indicates a waveform at the time when an automobilecollides with a pedestrian and a broken line indicates a waveform at thetime when the automobile collides with a fixed object. When theautomobile collides with a pedestrian, bumper 30 and substrate 11 aredeformed suddenly, wire 13 is pulled, and tension increases rapidly.Thereafter, the pedestrian is sent flying and the deformation ofsubstrate 11 does not progress any more. Therefore, wire 13 undergoes achange while keeping stress corresponding to an amount of deformation ofsubstrate 11 in a state in which the pedestrian is sent flying. Thus, achange in tension increases rapidly at an instance of the collision and,after that, fixed tension is kept.

When the change is considered in terms of an output with a DC componentcut from the viewpoint of detection circuit 23, the change representsthe amount of change in tension, that is, a differential amount. Anamount of change in output also increases rapidly according to the rapidincrease in tension generated at an instance of the collision with thepedestrian. Since tension becomes constant as the pedestrian is sentflying, the amount of change decreases rapidly to reach 0 finally.Therefore, a waveform of the output has a peak as indicated by the solidline in FIG. 5.

When the automobile collides with a fixed object, as in the case of thecollision with the pedestrian, first, substrate 11 is deformed suddenlyand wire 13 is pulled, and tension increases rapidly. Thereafter, sincethe fixed object is not sent flying, substrate 11 continues to bedeformed until the automobile stops or is bounced back by the fixedobject. Therefore, wire 13 continues to extend over a long time bytension larger than the tension in the state in which the pedestrian issent flying. Finally, wire 13 undergoes a change while keeping tensionaccording to an amount of deformation of substrate 11. Thus, a change intension increases rapidly to a value larger than that in the case ofcollision with the pedestrian at an instance of the collision and, afterthat, continues to increases more slowly than at the time of thecollision. Finally, fixed tension is kept.

When the change is considered in terms of an output with a DC componentcut from the viewpoint of detection circuit 23, an amount of change inoutput also increases rapidly according to the rapid increase in tensioncaused at an instance of the collision with the fixed object. Whenbumper 30 and substrate 11 continue to be deformed, an amount of changein tension decreases gently. When the automobile stops or is bouncedback, the deformation of substrate 11 stops and tension becomesconstant. Thus, the mount of change finally reaches 0. Therefore, awaveform of an output has a peak and gently decreases as indicated by adotted line in FIG. 5.

It is possible to distinguish collision with a human and collision withan object from each other using such a difference in outputcharacteristics. An algorithm for that purpose is shown in a flowchartin FIG. 6. Note that the software is executed by a microcomputer (notshown) built in detection circuit 23. First, the microcomputer reads anoutput with a DC component cut of tension sensor 14 (S1). Themicrocomputer compares the output with an output value of the last time(S2). If there is no change in the output value, since collision has notoccurred (No in S2), the microcomputer updates the value read this timeas the last value (S3). Thereafter, the microcomputer returns to S1.

When the output value changes in S2 (Yes in S2), since some collisionhas occurred in bumper 30 integrated with substrate 11, themicrocomputer continuously reads a change in tension sensor 17 afterthat for a defined time (S4). The defined time is determined bycalculating time equivalent to T shown in FIG. 5 in advance from anoutput characteristic of tension sensor 14 at the time when a pedestriandummy is caused to collide with an automobile having a bumper collisionsensor built therein. After reading an output for the defined time, themicrocomputer searches for a maximum value and judges whether the valueis within a defined range (a maximum value range of an output waveformcalculated by causing the pedestrian dummy to collide with bumper 30 asdescribed above) (S5).

When the maximum value is within the defined range (Yes in S5), themicrocomputer compares an absolute value of output attenuation speedafter the maximum value and a defined value (an attenuation speedabsolute value of an output waveform calculated from the pedestriandummy) (S6). When the absolute value is larger than the defined value(Yes in S6), the microcomputer judges that bumper 30 has collided with apedestrian and outputs a magnitude of the maximum value as a magnitudeof deformation of bumper 30 with a digital signal (S7). Themicrocomputer informs a system side that bumper 30 has collided with thepedestrian by outputting the value. On the other hand, when it is judgedin S5 that the maximum value is outside the defined range (No in S5) orit is judged in S6 that the absolute value is smaller than the definedvalue (No in S6), the microcomputer judges that bumper 30 has collidedwith a fixed object and outputs a fixed object collision flag for, forexample, decrementing a value of the magnitude of deformation by one(S8).

As described above, the bumper collision sensor performs judgment ofcollision in the detection circuit 23. Consequently, it is possible toeliminate an influence of disturbance noise on wiring between tensionsensor 14 and the pedestrian protection system as in the case in whichan output of tension sensor 14 is directly sent to the pedestrianprotection system as an analog value. As a result, high reliability isobtained and burden on the software of the pedestrian protection systemis reduced.

When bumper 30 collides with a pedestrian, since a magnitude ofdeformation of bumper 30 is outputted digitally, the bumper collisionsensor is not affected by noise as described above and reliability isimproved. Moreover, it is possible to directly judge on the pedestrianprotection system side whether bumper 30 has collided with an adult or achild from a matrix of a magnitude of deformation and vehicle speed atthe time of collision calculated from a collision test using apedestrian dummy in advance. Thus, it is possible to easily performoptimum expansion control for an airbag corresponding to the judgment.

With the constitution and the operations described above, it is possibleto obtain a bumper collision sensor that can detect collision with highreliability without hurting a pedestrian even if bumper 30 and substrate11 are deformed significantly.

Note that, although substrate 11 is integrally fixed to bumper 30 withan adhesive or the like in the explanation of this embodiment, asubstrate may be a bumper.

Second Embodiment

FIG. 7 is a schematic perspective view of a bumper collision sensor in asecond embodiment of the invention. FIG. 8A is a diagram of a state inwhich wires are fit in between projections of the bumper collisionsensor in this embodiment. FIG. 8B is a diagram of a state in which awire holding member is fit in between the projections of the bumpercollision sensor in this embodiment. FIG. 8C is a diagram of a state inwhich a heat press is applied to the projections of the bumper collisionsensor in this embodiment. FIG. 8D is a diagram of a state in whichintegration of the wire holding member in the projections of the bumpercollision sensor in this embodiment is completed. FIG. 9 is a partialsectional view showing a structure of a tension sensor in the bumpercollision sensor in this embodiment. FIG. 10A is a diagram of a wirestate at normal time in a schematic diagram showing a wire deformationpattern according to a collision position in the bumper collision sensorin this embodiment. FIG. 10B is a diagram of a wire state upon a leftside collision in the schematic diagram of the bumper collision sensorin this embodiment. FIG. 10C is a diagram of a wire state at centercollision time in the schematic diagram of the bumper collision sensorin this embodiment. FIG. 10D is a diagram of a wire state at upon aright-side collision in the schematic diagram of the bumper collisionsensor in this embodiment. FIG. 10E is a diagram of a wire state uponleft and center collisions in the schematic diagram of the bumpercollision sensor in this embodiment. FIG. 10F is a diagram of a wirestate upon left and right collisions in the schematic diagram of thebumper collision sensor in this embodiment. FIG. 10G is a diagram of awire state upon center and right collisions in the schematic diagram ofthe bumper collision sensor in this embodiment. FIG. 10H is a diagram ofa wire state upon left, center, and right collisions in the schematicdiagram of the bumper collision sensor in this embodiment.

FIG. 11 is a flowchart showing operations of the bumper collision sensorin this embodiment. In FIG. 7, FIGS. 8A to 8D, and FIG. 9, componentsthat are the same as those in FIG. 1, FIGS. 2A to 2D, and FIG. 3,respectively, are denoted by the same reference numerals. Explanationsof such components are omitted.

A characteristic of the bumper collision sensor in this embodiment shownin FIG. 7 is different from the constitution of the first embodimentshown in FIG. 1 in that plural (four in FIG. 7) wires 13 with lengthsdifferent from one another are arranged in parallel to a longitudinaldirection of substrate 11. The number of projections 12 is increased andwire holding members 15 are extended in association with the increase inthe number of wires 13 such that all wires 13 can beheld. Tensiondetecting units (not shown), equal in number to the wires 13, are builtin tension sensor 14. Substrate 11 also serves as a bumper.

With such a constitution, for example, in FIG. 7, when a pedestriancollides with the right side of substrate 11 also serving as a bumper,since all four wires 13 are pulled, all four outputs of the tensiondetecting units change. On the other hand, when a pedestrian collideswith the left side of the substrate 11, since only the longest wire 13(a wire at the top in FIG. 7) is pulled, only an output of the tensiondetecting unit to which the top wire 13 is connected changes. Therefore,by adopting the constitution shown in FIG. 7, a new function is added inthat it is possible to judge which position of the bumper a pedestriancollides with.

As shown in FIGS. 8A to 8D, a method of integrating wires 13 insubstrate 11 of such a bumper collision sensor has substantially thesame procedures as those shown in FIG. 2. FIGS. 8A to 8D show a sectionof a dotted line part in FIG. 7. In the example in FIGS. 8A to 8D, inorder to hold four wires 13, five projections 12 are provided for eachof wire holding members 15, wire holding members 15 are extended inassociation with the increase in the number of projections 12, and thenumber of not-shown holes is also increased to five. It is possible tointegrate the four wires 13 with substrate 11 at the same time in thesame process as in the first embodiment by fixing these with heat press16 simultaneously as in the first embodiment.

An internal structure of tension sensor 14 is shown in FIG. 9.Basically, the number of tension sensors 14 may be increased to four inassociation with the increase in the number of wires 13 to four. Asshown in FIG. 9, it is possible to form four tension detecting units 17on the same row from one stainless steel substrate 20 by providing fourbeams constituting tension detecting units 17 on stainless steelsubstrate 20. With such a constitution, space efficiency of tensionsensor 14 is improved. Production efficiency is improved by formingstrain resistance elements 22 at the same time through printing andsintering processes. In addition, it is possible to provide the fourtension detecting units 17 with less fluctuation.

Moreover, it is possible to form a common detection circuit 23 in rootportions of the four beams. It is possible to share the judgment by themicrocomputer. Thus, compared with the case in which the four tensionsensors are provided separately, the provision of detection circuit 23is simplified. It is possible to improve reliability and reduce costthrough reduction in the number of components.

Operations in this embodiment will be explained. Note that a vehiclespeed range as a premise of the operations is set to 20 to 60 km perhour as in the first embodiment. Outputs of respective tension detectingunits 17 at the time when a pedestrian or a fixed object collides withsubstrate 11 also serving as the bumper are the same as those shown inFIG. 5. An operation for detecting a collision position, which is acharacteristic of the second embodiment, will be explained.

FIGS. 10A to 10H are schematic diagrams of substrate 11 viewed from thedirection shown by an arrow in FIG. 7. In FIGS. 10A to 10H, four wires13 are indicted by bold lines. In order to distinguish respective wires13, wires 13 are defined as wire 131, wire 132, wire 133, and wire 134in order from the longest one provided at the top part of substrate 11.Tension detecting units 17 connected to respective wires 13 cut anoutput of a DC component with a filter (not shown) provided in detectioncircuit 23 in order to avoid influences of aged deterioration andtemperature change as in the first embodiment.

In a normal (non-collision) state shown in FIG. 1A, since substrate 11is not deformed, tension is not applied to respective wires 13.Therefore, all outputs of respective tension detecting units 17 arezero. When a pedestrian collides with the left of substrate 11, the leftside of substrate 11 is deformed as shown in FIG. 10B. The deformationis represented as a downward dent. Deformation is represented in thesame manner in the other figures. In this case, only wire 131 is pulledbecause of the deformation. When an integral value (an area) of awaveform indicated by a solid line in FIG. 5 at that point is assumed tobe 1, a ratio of outputs that are integral values of waveforms ofrespective tension detecting units 17 is 1:0:0:0. The ratio is shown onthe right side of tension sensor 14 in FIG. 10B. Ratios are shown in thesame manner in the other figures.

When a pedestrian collides with the center of substrate 11, the centerof the substrate 11 is deformed as shown in FIG. 10C. In this case,wires 131, 132, and 133 are pulled. When a degree of the pull isrepresented as a ratio of output integral values of respective tensiondetecting units 17, the ratio is 1:1:0.5:0. Similarly, when a pedestriancollides with the right of substrate 11, the right side of the substrate11 is deformed as shown in FIG. 10D and all wires 13 are pulled. A ratioof output integral values of respective tension detecting units 17 is1:1:1:1. From the above, it is possible to learn with which part ofsubstrate 11 the pedestrian collides according to a ratio of outputintegral values of respective tension detecting units 17.

Note that, although there are four different length wires 13 in thisembodiment, a larger number of wires with more finely varied lengths maybe provided. Consequently, it is possible to further improve positiondetection accuracy.

In the constitution in FIG. 7, it is also possible to learn positionswhen plural pedestrians collide with substrate 11 simultaneously. FIG.10E shows a case in which pedestrians collide with the left and thecenter of substrate 11 simultaneously. In this case, since the left sideand the center of the substrate 11 are deformed, wires 13 arranged inthe portions are pulled. Since wire 131 is pulled in two places, anoutput integral value of tension detecting units 17 is about twice aslarge as that in one place. On the other hand, the other wires 132, 133,and 134 are pulled in the same manner as the case in which a pedestriancollides with only the center of substrate 11, a ratio of outputintegral values of respective tension detecting units 17 is 2:1:0.5:0.

Similarly, when pedestrians collide with the left and the right ofsubstrate 11 simultaneously, as shown in FIG. 10F, a ratio of outputintegral values of respective tension detecting units 17 is 2:1:1:1.When pedestrians collide with the center and the right side of substrate11 simultaneously, as shown in FIG. 10G, a ratio of output integralvalues of respective tension detecting units 17 is 2:2:1.5:1. When threepedestrians collide with substrate 11 simultaneously, since the left andthe right and the center of substrate 11 are deformed as shown in FIG.10H, a ratio of output integral values of respective tension detectingunits 17 is 3:2:1.5:1. The eight types of collision patterns includingthat in a normal (non-collision) state are described. It is seen thatthe ratios of output integral values are different from one another.Therefore, it is possible to learn how many pedestrians collide withwhich parts of substrate 11 by calculating a ratio of output integralvalues.

Note that a reason for using output integral values is as describedbelow. When a maximum value of outputs described in the first embodimentis used, a maximum value corresponding to the number of colliding peopleis obtained if plural pedestrians collide with substrate 11 completelysimultaneously. However, if there are slight time differences amongcollisions of the pedestrians, since plural peak values appear, amaximum value proportional to the number of colliding people is notalways obtained. On the other hand, when an integral value of a waveformis used, a maximum value is low even if there are time differences.Thus, it is possible to calculate the number of colliding people moreaccurately compared with the detection of a maximum value because awidth of a waveform is increased.

Therefore, when one pedestrian collides with substrate 11, it ispossible to use a maximum value as a magnitude of deformation ofsubstrate 11 as in the first embodiment even if outputs are notintegrated. It is also possible to learn a collision position accordingto the tension detecting unit 17 for which the maximum value isobtained. When a judgment output assuming collision with pluralpedestrians is obtained, it is advisable to use a ratio of outputintegral values. On the basis of the operations described above, analgorithm of operations in the second embodiment is shown in a flowchartin FIG. 11. Note that the software is also executed by the microcomputer(not shown) built in detection circuit 23 as in the first embodiment.

First, the microcomputer reads outputs with DC components cut ofrespective tension detecting units 17 (S11). The microcomputer comparesthe outputs with output values of the last time (S12). If there is nochange in the output values, since collision has not occurred (No inS12), the microcomputer updates the values read this time as the lastvalues, respectively (S13). Thereafter, the microcomputer returns toS11. When any one of the output values changes in S12 (Yes in S12),since some collision has occurred in substrate 11, the microcomputercontinuously reads changes in respective tension detecting units 17after that for a defined time (S14) A method of determining the definedtime is the same as that in the first embodiment.

After reading outputs for the defined time, the microcomputer searchesfor maximum values of the respective outputs and judges whether thevalues are within a defined range that is a maximum value range of anoutput waveform calculated by causing the pedestrian dummy to collidewith substrate 11 (S15). When the maximum values are within the definedrange (Yes in S15), the microcomputer compares absolute values of outputattenuation speed after the maximum values and a defined value that isan attenuation speed absolute value of an output waveform calculatedfrom the pedestrian dummy (S16). When the absolute values are largerthan the defined value (Yes in S16), the microcomputer judges thatsubstrate 11 has collided with pedestrians, calculates maximum values ofrespective tension detecting units 17, and integrates output values(S17).

The microcomputer outputs magnitudes of the maximum values as magnitudesof deformation of substrates 11 also serving as the bumper with adigital signal and outputs collision positions and the number ofcolliding people by comparing a ratio of the respective integral valueswith the pattern shown in FIG. 10 (S18). Note that, since the magnitudesof deformation of substrate 11 are outputted digitally, a system side isinformed that substrate 11 has collided with the pedestrian. On theother hand, when it is judged in S15 that the maximum values are outsidethe defined range (No in S15) or it is judged in S16 that the absolutevalues are smaller than the defined value (No in S16), the microcomputerjudges that substrate 11 has collided with a fixed object and outputs afixed object collision flag for, for example, decrementing values of themagnitudes of deformation by one (S19).

As described above, the bumper collision sensor performs judgment ofcollision in the detection circuit 23. Consequently, it is possible toeliminate an influence of disturbance noise on wiring and thereforereliability is improved as in the first embodiment. Moreover, the bumpercollision sensor outputs collision positions and the number of collidingpeople. Consequently, in a pedestrian protection system having pluralairbags, the burden on the software for controlling optimum expansion ofthe airbags close to the collision positions is reduced. It is possibleto perform optimum expansion control for the airbags as the pedestrianprotection system as a whole including judgment on an adult or a childby the digital output of magnitudes of deformation of substrate 11 alsoserving as the bumper.

With the constitution and the operations described above, it is possibleto obtain a bumper collision sensor that can detect how many peoplecollide with which parts of substrate 11 with high reliability withouthurting pedestrians even if substrate 11 also serving as the bumper isdeformed significantly.

Third Embodiment

FIG. 12 is a schematic perspective view of a bumper collision sensor ina third embodiment of the invention. FIG. 13A is a diagram of a wire ina normal (non-collision) state in a schematic diagram showing a wiredeformation pattern according to a collision position in the bumpercollision sensor in this embodiment. FIG. 13B is a diagram of a wirestate upon a left collision in the schematic diagram of the bumpercollision sensor in this embodiment. FIG. 13C is a diagram of a wirestate upon a center collision in the schematic diagram of the bumpercollision sensor in this embodiment. FIG. 13D is a diagram of a wirestate upon a right collision in the schematic diagram of the bumpercollision sensor in this embodiment. FIG. 13E is a diagram of a wirestate upon left and center collisions in the schematic diagram of thebumper collision sensor in this embodiment. FIG. 13F is a diagram of awire state upon left and right collisions in the schematic diagram ofthe bumper collision sensor in this embodiment. FIG. 13G is a diagram ofa wire state upon center and right collisions in the schematic diagramof the bumper collision sensor in this embodiment. FIG. 13H is a diagramof a wire state upon left, center, and right collisions in the schematicdiagram of the bumper collision sensor in this embodiment.

In FIG. 12 and FIGS. 13A to 13H, components that are the same as thosein FIG. 1 and FIGS. 10A to 10H, respectively, are denoted by the samereference numerals. Explanations of such components are omitted. Acharacteristic of the bumper collision sensor in the third embodimentshown in FIG. 12 is that the bumper collision sensor includes a pair ofbumper collision sensors with the same constitution as in the secondembodiment shown in FIG. 7, tension sensor 14R of one of the bumpercollision sensors is mounted on a position of a bumper shown on an upperright side in FIG. 12, and tension sensor 14L of the other of the bumpercollision sensors is mounted on a position of the bumper shown on alower left side in FIG. 12.

In order to mount respective bumper collision detecting units built inthe pair of tension sensors 14R and 14L with high space efficiency, asshown in FIG. 12, wires 13 are arranged such that a relation betweenwires is reversed, for example, in a place where one wire 13 is long,the other wire 13 is arranged short. Consequently, it is possible tomount the pair of bumper collision sensors on a substrate also servingas a bumper by simply adding one or more stages of projections 12 inaddition to those in FIG. 7. Note that, although a structure in whichonly a part of wires 13 are tension springs is shown in FIG. 12, allwires 13 may be tension springs as described in the first and the secondembodiments. Also wires 13 in the first and the second embodiments maybe only part tension springs. Although the substrate is the bumper inthe explanations of the second and the third embodiments, the substratemay be attached to the bumper as in the first embodiment. A method ofattaching the substrate is not limited to a method using an adhesive. Itis also possible that a groove is provided and the substrate is fit inthe groove. Alternatively, the substrate is attached by high-frequencywelding or may be fixed by plastic rivets. Moreover, a material of thesubstrate and a plastic property thereof may be identical with ordifferent from those of the bumper.

By adopting the constitution in this embodiment, since two tensionsensors 14 are provided, even if one tension sensor 14 or tensiondetecting unit 17 built in tension sensor 14 breaks down, an output isobtained by the other tension sensor 14 as explained with reference toFIGS. 10A to 10H. Thus, reliability of the entire pedestrian safetysystem is extremely improved. This point will be explained in detailwith reference to FIGS. 13A to 13H. FIGS. 13A to 13H are, like FIGS. 10Ato 10H, schematic diagrams showing wire deformation patterns accordingto collision positions of the bumper collision sensor viewed in thedirection of the arrow shown in FIG. 12. Two sets of wires 13 are shownwith different line thicknesses such that wires 13 can be distinguishedfrom one another in the figures.

In order to distinguish all wires 13, wires 13 connected to tensionsensor 14R fixed to the right side of the bumper are defined as wire131R, wire 132R, wire 133R, and wire 134R in order from the longest oneprovided at the top part of substrate 11.

Wires 13 connected to tension sensor 14L fixed to the left side of thebumper are defined as wire 132L, wire 133L, wire 134L, and wire 135L inorder from the shortest one provided at the top part of substrate 11.For consistency of numbering, wires in the same position in a rowdirection are given the same number and distinguished by characters Land R. Note that there is no wire on the L side corresponding to longestwire 131R and a wire on the R side corresponding to longest wire 135L.

As in FIG. 10, numbers shown on the left and the right of substrate 11represent a ratio of output integral values of respective tensiondetecting units 17 built in tension sensors 14. In a normal(non-collision) state shown in FIG. 13A, since substrate 11 is notdeformed, tension is not applied to respective wires 13. Therefore, alloutputs of respective tension detecting units 17 are zero.

When a pedestrian collides with the left of substrate 11 also serving asthe bumper, the left side of substrate 11 is deformed as shown in FIG.13B. In this case, only wire 131R among wires 13 connected to tensionsensor 14R on the right side is pulled by deformation. On the otherhand, all wires 13 (132L, 133L, 134L, and 135L) connected to tensionsensor 14L on the left side are pulled. Therefore, a ratio of outputintegral values of respective tension detecting units 17 on the rightside is 1:0:0:0 and a ratio of output integral values of respectivetension detecting units 17 on the left side is 1:1:1:1.

Similarly, when a pedestrian collides with the center of substrate 11,as shown in FIG. 13C, a ratio on the right side is 1:1:0.5:0 and a ratioon the left side is 0:0.5:1:1. When a pedestrian collides with the rightof substrate 11, as shown in FIG. 13D, a ratio on the right side is1:1:1:1 and a ratio on the left side is 0:0:0:1.

Similarly, when plural pedestrians collide with the left and the centerof substrate 11, as shown in FIG. 13E, a ratio on the right side is2:1:0.5:0 and a ratio on the left side is 1:1.5:2:2. When pluralpedestrians collide with the left and the right of substrate 11, asshown in FIG. 13F, a ratio on the right side is 2:1:1:1 and a ratio onthe left side is 1:1:1:2. When plural pedestrians collide with the rightand the center of substrate 11, as shown in FIG. 13G, a ratio on theright side is 2:2:1.5:1 and a ratio on the left side is 0:0.5:1:2. Whenplural pedestrians collide with the left and the right and the center ofsubstrate 11, as shown in FIG. 13H, a ratio on the right side is3:2:1.5:1 and a ratio on the left side is 1:1.5:2:3.

In this way, two sets of ratios of output integral values are obtainedaccording to respective states of collision. Therefore, in the secondembodiment, when one of tension detecting units 17 breaks down anddeviates from the eight patterns of ratios of output integral valuesshown in FIGS. 10A to 10H, it is impossible to learn in which state apedestrian actually collided with substrate 11. However, in the thirdembodiment, another set of ratios of output integral values areobtained. Thus, if any one of the patterns matches a state of collision,extremely high reliability against failure is obtained by outputting thestate of collision. Note that an algorithm of operations is the same asthat shown in FIG. 11.

Moreover, by adopting the constitution, there is an effect that, forexample, even when substrate 11 collides with a pedestrian near a cornerof a building, the possibility of pedestrian detection is improved. Thispoint will be explained in detail below. For example, a case in which acorner of a building collides in offset with the right side of substrate11 also serving as the bumper and the left side of substrate 11 hits apedestrian near the corner of the building is considered. In thestructures in the first and the second embodiments, since tension sensor14 is fixed to the right end of substrate 11, when substrate 11 collideswith a corner of a building, tension sensor 14 itself is destroyed. Itcould be difficult to detect a pedestrian colliding with the substrate11 simultaneously.

On the other hand, in the third embodiment, even if tension sensor 14Ron the right side is destroyed, tension sensor 14L on the left sidecontinues to operate. In this case, a waveform of an output of tensiondetecting unit 17 connected to long wires 133L, 134L, and 135L changesto a waveform as indicated by the dotted line in FIG. 5 because of thecollision with the building. Thus, it is judged that substrate 11collides with a fixed object. However, since a waveform of only shortestwire 132L changes to a waveform as indicated by the solid line in FIG.5, it is possible to learn that substrate 11 collides with a human. Inthis case, in a system having plural hood airbags, an airbag in aportion colliding with the building is destroyed or, even if the airbagis not destroyed, it is unnecessary to expand the airbag because thereis no pedestrian. It is also unnecessary to judge collision positionsand the number of collisions. Only an airbag on the left side ofsubstrate 11 colliding with the human has to be expanded. According tosuch an operation, even if one tension sensor 14 is destroyed bycollision, the possibility that collision of a pedestrian can bedetected by the other tension sensor 14 is improved.

With the constitution and the operations described above, it is possibleto obtain a bumper collision sensor that can detect how many peoplecollide with which parts of substrate 11 with high reliability withouthurting pedestrians even if substrate 11 also serving as the bumper isdeformed significantly.

Note that a movable body on which the bumper collision sensor of theinvention is mounted is not limited to an automobile. An object withwhich the movable body collides is not limited to a human in a walkingstate and may be a human riding an object having strength of the samedegree as a human or may be other animals.

According to the constitution described above, it is possible to detectextension of the extendable portion corresponding to deformation of thebumper and the substrate due to collision as tension of the wire withthe tension sensor. It is possible to detect collision without hurting apedestrian even if the bumper is deformed significantly.

1. A bumper collision sensor comprising: a wire having an extendableportion in a part thereof; a tension sensor connected to one end of saidwire; and a substrate that is mounted with said tension sensor and saidwire and attached, with plasticity, to a bumper; wherein said tensionsensor is fixed to one end of said substrate; wherein said wire isarranged in said tension sensor along a longitudinal direction of saidsubstrate with a stress equal to or lower than a value set in advance;wherein the other end of said wire is fixed to said substrate; andwherein said extendable portion of said wire is a tension spring.
 2. Thebumper collision sensor of claim 1, wherein said wire is made ofstainless steel.
 3. A bumper collision sensor comprising: a wire havingan extendable portion in a part thereof; a tension sensor connected toone end of said wire; and a substrate that is mounted with said tensionsensor and said wire and attached, with plasticity, to a bumper; whereinsaid tension sensor is fixed to one end of said substrate; wherein saidwire is arranged in said tension sensor along a longitudinal directionof said substrate with a stress equal to or lower than a value set inadvance; wherein the other end of said wire is fixed to said substrate;wherein plural projections are formed integrally with said substrate;and wherein a wire holding member for holding said wire is fixed to saidprojections.
 4. The bumper collision sensor of claim 3, wherein sectionsof said projections are circular.
 5. The bumper collision sensor ofclaim 3, wherein a section of said wire holding member is circular. 6.The bumper collision sensor of claim 3, wherein holes are provided in apart of said wire holding member, and said projections pass through saidholes, respectively, and said wire holding member is fixed to saidprojections by deformed parts of said projections.
 7. The bumpercollision sensor of claim 3, wherein said wire is fixed to a part ofsaid projections formed integrally with said substrate.
 8. A bumpercollision sensor comprising: a wire having an extendable portion in apart thereof; a tension sensor connected to one end of said wire; and asubstrate that is mounted with said tension sensor and said wire andattached, with plasticity, to a bumper; wherein said tension sensor isfixed to one end of said substrate; wherein said wire is arranged insaid tension sensor along a longitudinal direction of said substratewith a stress equal to or lower than a value set in advance; wherein theother end of said wire is fixed to said substrate; and wherein saidtension sensor includes a strain resistance element, a resistance ofwhich changes because of distortion.
 9. The bumper collision sensor ofclaim 8, wherein said strain resistance element comprises a printed andsintered thick-film resistor paste containing ruthenium oxide conductiveparticles and a glass component.
 10. The bumper collision sensor ofclaim 8, wherein said tension sensor includes a detection circuit, andsaid detection circuit is formed on a stainless steel substrate togetherwith said strain resistance element.
 11. The bumper collision sensor ofclaim 10, wherein said detection circuit judges, when a maximum value ofa changing component obtained by excluding a DC component from a changein a voltage due to a change in a resistance of said strain resistanceelement is within a defined range and an attenuation speed absolutevalue of the changing component is equal to or larger than a definedvalue, that the bumper has collided with a pedestrian and outputs themaximum value as a magnitude of deformation of the bumper.
 12. A bumpercollision sensor comprising: a wire having an extendable portion in apart thereof; a tension sensor connected to one end of said wire; and asubstrate that is mounted with said tension sensor and said wire andattached, with plasticity, to a bumper; wherein said tension sensor isfixed to one end of said substrate; wherein said wire is arranged insaid tension sensor along a longitudinal direction of said substratewith a stress equal to or lower than a value set in advance; wherein theother end of said wire is fixed to said substrate; wherein said wire isone of a plurality of wires arranged in parallel and mounted with saidsubstrate; wherein said tension sensor is one of a plurality of tensionsensors connected to respective ends of said wires; and wherein lengthsof the respective wires are set to be different from one another. 13.The bumper collision sensor of claim 12, wherein said tension sensorsare in parallel with each other and integrally formed.
 14. The bumpercollision sensor of claim 12, wherein said tension sensors includedetection circuits, said detection circuits judge, when maximum valuesof changing components obtained by excluding DC components from changesin voltages due to changes in resistances of respective ones of saidstrain resistance elements are within a defined range and attenuationspeed absolute values of the changing components are equal to or largerthan a defined value, that the bumper has collided with pedestrians andoutput the maximum values as magnitudes of deformation of the bumper,and said detection circuits calculate collision positions and the numberof colliding people from a value obtained by integrating the respectivechanging components and output the collision positions and the number ofcolliding people.
 15. A bumper collision sensor comprising a pair ofbumper collision sensors of claim 12, wherein one of said tensionsensors is mounted on one end of said substrate and the other of saidtension sensors is mounted on the other end of said substrate.
 16. Thebumper collision sensor of claim 1, wherein the substrate is the bumper.17. The bumper collision sensor of claim 3, wherein said extendableportion of said wire is a tension spring.
 18. The bumper collisionsensor of claim 8, wherein said extendable portion of said wire is atension spring.
 19. The bumper collision sensor of claim 12, whereinsaid extendable portion of each of said wires is a tension spring.